• 73 - A radiotelegraph code meaning "Best regards, Best wishes, or Good luck." Used toward the end of a contact.

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• Absorption - The reduction in a radio signal strength due to refraction in the ionosphere.

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• AllStar - A software-based system that links ham radio stations around the world through your cell phone or other computing device using VoIP.

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• Amateur frequency band - A portion of the frequency (radio) spectrum internationally allocated to amateur radio and amateur satellite use. 

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• Amplitude - The strength of a signal, it is the height of a wave from the average position.

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• Antenna - a rod, wire, or other device used to transmit or receive radio or television signals.

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• Antenna gain - The ability of the antenna to radiate more or less in any direction compared to a theoretical antenna. If an antenna could be made as a perfect sphere, it would radiate equally in all directions.

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• Antenna tuner - Also referred to as an ATU, an antenna tuner is a device that matches the impedance of the antenna system with that of the transceiver to maximize power transfer from the transmitter to the antenna. The term AMU (Antenna matching unit) is also sometimes used to describe this type of unit.

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• ASL (Above sea level) - the vertical height in feet (ft) or meters (m) above sea level.

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• Attenuation - is a reduction of signal strength during transmission.

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• Azimuth - The term azimuth is commonly found in reference to “the horizon” or “the horizontal” whereas the term elevation commonly refers to “the vertical”. When used to describe antenna patterns, these terms assume that the antenna is mounted (or measured) in the orientation in which it will be used. 

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• Band conditions - Atmospheric (weather, etc.), geomagnetic, solar, and other activities that could have an affect on the radio frequency (RF) propagation for a particular band.

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• Bandwidth (BW) - A range of frequencies within a given band, in particular that used for transmitting a signal.

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• Band-stop filter - A filter containing a circuit that passes all frequencies with the exception of those within a specified stop band which are greatly attenuated.

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• Balun (balanced-to-unbalanced) - A simple transformer used to change an unbalanced input to a balanced output. It is part of an antenna system that provides the transition between a balanced antenna such as as centre fed dipole and an unbalanced transmission line such as coaxial cable, or dipole to coax.

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• Beam antenna - A directional antenna or beam antenna is an antenna which radiates or receives greater radio wave power in specific directions. The antenna must be able to rotate in order to provide coverage in all the different directions.

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• Capacitance - The ability of a component or circuit to collect and store energy in the form of an electrical charge, expressed in the unit of farads (F).

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• Chirp - (CW term) A slight shift in transmitter frequency each time the transmitter key is operated that results in a chirping sound. Also sometimes referred to as key clicks. 

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• Clansman - Clansman is the name of a combat net radio system (CNR) used by the British Army from 1976 to the early 2000’s when it was replaced by Bowman communication system. Today they are very popular amongst amateur operators and even have their own nets where like minded people communicate via the radios.

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• Clipping - Overdriving an amplifier circuit, causing the signal to drop out on voice peaks. Also known as clip-distortion; flat topping; flat-topping.

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• CW - Radio communication by Morse code, this was the only way to communicate for the first decade or more of Amateur Radio.

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• D layer - The lowest region of the ionosphere. The D-layer contributes very little to short-wave radio propagation and acts mainly to absorb energy from radio waves as they pass through it. This absorption has a significant effect on signals below about 7.5 megahertz (MHz) during daylight. Also known as D region.

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• End-fed - Used to describe an antenna design whose feedline connects to one end of a radiating element. Commonly found in monopoles, J-poles, or even a random wire configuration, it can also be referred to as an end-fed half-wave (EFHW).

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• E-layer - The region of the ionosphere found approximately 55 to 90 miles above Earth, the second lowest ionospheric layer. This region fades away a few hours after sunset. The main impact of the E-layer on radio propagation is to absorb energy from signals passing through it. Although sporadic, E propagation makes possible distant communication on frequencies above 30 megahertz (MHz). Also known as E region.

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• F layer - The region of the ionosphere found approximately 90 to 400 miles above Earth and which is responsible for most long distance propagation on frequencies below 30 megahertz (MHz). The F-layer refracts radio waves and returns them to Earth. During the daytime, especially in the summer, solar heating can cause the F-layer to split into two separate layers, the F1-layer and the F2-layer. Also known as F region.

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• Ground wave - An electrical wave traveling directly from the transmitter to the receiving station without bouncing off the ionosphere, can also known as surface wave.

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• HEMA - Stands for HuMPs Excluding Marilyns Award. A HuMP is a summit that has Hundred Metre Prominence, meaning that it sticks up above the surrounding land by at least 100m. A Marilyn is a summit with 150m prominence. (http://www.hema.org.uk/)

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• HF (High-frequency bands) - Amateur radio bands in the region of the radio frequency (RF) spectrum from 3 to 30 megahertz (MHz). 

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• Inductance - The property of an electric conductor or circuit that causes an electromotive force to be generated by a change in the current flowing. A measure of the ability of a coil to store energy in a magnetic field.

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• Impedance - The opposition of both the electrical alternating current (AC) and direct current (DC) in a circuit. 

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• Ionosphere - A region of electrically charged or ionized gases high in the atmosphere. The ionosphere bends radio waves as they travel through it, returning them to Earth. Also known as sky-wave propagation.

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• Lightning arrestor - A device used to protect against transient voltages, normally caused by lightning strikes or back EMF from capacitive or inductive loads are present. The typical lightning arrester has a high-voltage terminal and a ground terminal, when a lightning surge (or switching surge, which is very similar) travels along the power line to the lightning arrester, the current from the surge is diverted through the arrestor, in most cases to earth. 

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• Line-of-sight - Mainly thought of for line of sight propagation. The term used to describe very-high frequency (VHF) and ultra-high frequency (UHF) propagation in a straight line directly from one station to another. The rule of thumb sight + 1/3 for the distance of travel for the signal is used, past this repeater stations are needed.

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• Low band - Slang for high frequency (HF). 

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• Maidenhead Locator System - This is a geographic coordinate system of grid squares drawn on maps of the Earth and used by amateur radio operators. It was named after the town outside London where it was first conceived by a meeting of European very-high frequency (VHF) managers in 1980. 

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• NanoVNA - A small vector network analyser used to test amongst other things, the coax quality and length, he SWR of an antenna, the results of the smith chart for impedance etc. Using a stimulus signal from port 1, the signal is transported with 50 ohm characteristic impedance coaxial cable to a device under test. The frequency range of the stimulus signal can be anywhere in the range from 10 kHz to 1500 MHz

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• Net - A group of stations that meet on a specified frequency at a certain time. The net is organized and directed by a net control station operator, who calls the net to order, recognizes stations entering and leaving the net, and authorizes stations to transmit. 

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• Noise floor - The average power of the sum noise from all noise sources. A weak signal must be above the noise floor to be discernible.

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• PL259 - A UHF connector designed in the 1930s and is basically a 'Banana plug' with a threaded shielding around it. They are generally good to a frequency of 300MHz.

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• POTA (Parks On The Air) - is an amateur radio operating award program started in 2010 with its non-profit organization being founded in 2018 that encourages amateur radio operators to operate in a variety of parks and public lands as a portable station. Activations can take place during other events such as Field Day.

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• Propagation - The behaviour of radio waves when they are transmitted from one point on the Earth to the atmosphere or another point on earth. Radio propagation is affected by the daily changes of water vapor in the troposphere and ionization in the upper atmosphere, because of the effects of the Sun.

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• Q code - An abbreviation for a common term used on the air, some of which can also be used as a question when followed by a question mark (See the Q-Code tab above).

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• Rag chew - A term used by amateur radio operators to describe QSO's where they are chatting informally.

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• Repeater - Describes a receiver/transmitter that listens for a transmission on one frequency, usually a weak one, and re-transmits it, usually at higher power, on another frequency for extended communication. Repeaters are usually placed at high geographical locations for access by very-high frequency (VHF) and ultra-high frequency (UHF) hand-held and mobile transceivers to extend the range of a transmission. The separation between these two frequencies is referred to as the offset. 

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• RST Report - A signal report system of Readability, Strength, and Tone (See the RST tab above).

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• Shack - A radio shack is a room or structure used by a radio operator for housing radio equipment. Many 'shacks' are in living rooms or spare bedrooms but some have made good use of cellars and loft spaces. 

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• Sibilance - A hissing sound created during speech in a group of words through the repetition of ‘s’ sounds. For example, “Sarah’s silly sister swallowed her sweet.” The other station may comment on the noise through the transmitted audio which will be harder to understand.

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• Signal-strength meter (S-meter) - An S meter is an indicator often provided on communications receivers, such as amateur radio or shortwave broadcast receivers. Originally used in the early 20th century as part of the readability, strength, tone (RST) reporting code, this is an assessment of the received signal, based on a 9-point scale. The scale markings are derived from a system of reporting signal strength from S1 (faint, barely perceptible signals) to S9 (very strong signals) as part of the RST code.

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• Simplex - An operational mode in which transmit and receive frequencies are the same. Most often used when communicating directly between operators without the use or need for voice repeaters. 

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• skip - A radio phenomenon in which signals are reflected by the atmosphere and return to earth in unexpected places, far away from the normal reception zones. In between transmitter and receiver there is a zone where no transmissions can be heard. 

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• SO239 - The socket half of the PL259.

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• Solar flare - A sudden burst of high energy observed over the surface of the sun, ejecting clouds of electrons, ions, and atoms into space, and often followed by a large coronal mass ejection.

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• Solar wind - A stream of charged particles released from the upper atmosphere of the sun, consisting mostly of electrons, protons, and alpha particles, which can interfere with radio transmission.

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• SOTA  (Summits on the air) - The aim of SOTA is to encourage licensed amateur radio operators to operate temporarily from mountainous locations using any method of travel including hiking, mountain climbing, and cycling while operating their amateur radio station from the summits of hills and mountains (https://www.sota.org.uk/).

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• Sporadic E - This is the layer of the atmosphere located within the ionosphere and made from clouds of intense ionization that allow reception of VHF signals from long distances at times. Propagation mode using the E layer of the ionosphere and commonly associated with occasional, strong over-the-horizon signals on the 10-, 6-, and 2-meter bands.

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• Squelch (SQL) - A circuit that mutes the receiver when no signal is present, thereby eliminating band noise.​​

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• SWR - Standing Wave Ratio, It indicates whether there is an impedance mismatch between the load and the internal impedance on a radio frequency (RF) transmission line.

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• Transceiver - a device that can both transmit and receive communications, in particular a combined radio transmitter and receiver.

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• Troposphere - The region in Earth's atmosphere just above the Earth's surface and below the ionosphere.

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• Tropospheric ducting - A type of very-high frequency (VHF) propagation that can occur when warm air overruns cold air. It can also be referred to as tropo or simply ducting.

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• UHF (Ultra high frequency) - The frequency range of 300 to 3,000 megahertz (MHz).

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• Unun (Unbalanced to Unbalanced) - A device that matches the impedance of an unbalanced feedline (such as a coaxial cable) to that of another unbalanced one.

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• Voice over Internet Protocol (VoIP) - The communication protocols, technologies, methodologies, and transmission techniques involved in the delivery of voice communication and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. Also known as VOIP.

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• Volt (V) - The basic unit of electrical pressure or electromotive force (EMF) it signifies the difference of potential that would carry one ampere of current against one ohm resistance.

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• VHF (Very high frequency) - The frequency range of 30 to 300 megahertz (MHz).

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• Worked All Britain (WAB) - An award from the Worked All Britain (WAB) website to any amateur radio operator who confirms two-way communication with all of Britain's grid system units.

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• Waterfall display - A display on the front screen of a radio, used with digital modes of transmission that shows signal strength as a change of brightness with frequency represented by position on the line. When looking at the display older lines move down so that the history of the signal's strength and frequency form a waterfall-like picture.

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• Waveguide - A structure e.g. a metal tube or other device that is used for confining and conveying  microwaves electromagnetic waves.

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• Yagi antenna - The most popular type of directional antenna or beam antenna. It is a multi-element array in which one of the elements called the driven element is directly connected to feeder coax. Named after Hidetsugu Yagi who, along with Shintaro Uda, invented the array in 1926. Sometimes called the Yagi-Uda antenna, but most often shortened to Yagi.